Field of the Invention
The present invention relates to a lens system and an image capturing system including the lens system.
Description of the Related Art
Image capturing systems used for capturing images for television (referred to also as “TV lens system” below) include a television camera (simply referred to also as “camera device” below) and a TV lens (simply referred to also as “lens system” below).
A TV lens mainly includes a lens device and a drive unit. The lens device includes an image-capturing optical system and a manual adjustment ring for operating the image-capturing optical system.
The drive unit includes therein components such as a motor and a control board for electrically driving the manual adjustment ring, a central processing unit (CPU), and a position detection sensor. With this configuration, the TV lens system can perform high-precision position detection, and electric drive with high operability can be realized.
Meanwhile, image capturing systems for film, commercial, and drama productions (referred to also as “cinema lens systems” below) are known. Recent cinema lens systems, in which a drive unit is connected to a lens device as in TV lens systems, have operability equivalent to that of TV lens systems.
Camera devices included in some cinema lens systems have both a still-image capturing mode and a moving-image capturing mode. Especially in the still-image capturing mode, it is desired in some situations to capture an image immediately after the lens device is started. In view of such a situation, the time required from when the lens device is started to when the camera device is ready to start capturing an image is preset at an extremely short time so that users do not become stressed. In the following description, the time required from when the lens device is started to when the camera device is ready to start capturing an image is referred to also as “camera image-capturing start period.”
Some image capturing systems have a function of turning off functions of the lens device (referred to also as “low-power-consumption state” below) when no operation has been made in a certain period of time. Accordingly, the lens device of such image capturing systems is started from the low-power-consumption state or from the power-off state.
The camera device, for example, displays the lens position on the viewfinder (VF) and adjusts the light amount and the like on the basis of the lens position. To enable these operations, the lens device needs to output (transmit) the lens position to the camera device after the lens device has been started from the power-off state and before the end of the camera image-capturing start period.
Some patent documents disclose techniques for reducing the time required to reach an image-capturing ready state from system start.
For example, Japanese Patent Laid-Open No. 2008-252348 discloses a technique for driving a zoom lens to set a focal length at a predetermined length when a camera is turned on.
Japanese Patent Laid-Open No. 2000-307925 discloses a technique for outputting data in high-speed processing in communications between a camera device and a lens device even when no command is input.
However, the following problem arises. The lens device outputs, to the camera device, information on a lens position that is input by a drive unit (referred to also as “position detection device” below) including a position detection sensor. However, the lens device cannot output the lens position information to the camera device before the end of the camera image-capturing start period if the lens device needs to wait for the establishment of communication between the lens device and the position detection device (first communication path).
According to the known technique disclosed in Japanese Patent Laid-Open No. 2008-252348 above, the zoom lens needs to be driven first, which takes longer than the camera image-capturing start period.
According to the known technique disclosed in Japanese Patent Laid-Open No. 2000-307925 above, when communication between the camera device and the lens device has been established and communication (communication path) between the position detection device and the lens device has not been established, the lens device cannot output position information in the period from when the lens device is started to the end of the camera image-capturing start period. In an alternative method, a lens device including a position detection sensor outputs position information obtained by the lens device to the camera device. However, to enable this method, the position detection sensor needs to be included in the lens device, which increases the cost and the size of the lens device.